1. Field of Invention
This invention relates to quick release type clamps, specifically to clamps that are easily fitted to existing conventional hardware such as threaded shafts and bolts.
2. Prior Art
When things are fastened together with shaft type fasteners such as ordinary threaded bolts and nuts, it is often desirable to tighten and loosen the fastening means quickly and without tools. In the prior art, various "quick release" type clamps and mechanisms have been used, but these typically require special means to attach to the shaft to be fastened. It is desirable to have a quick release type mechanism which does not require a special shaft or modifications to an existing shaft.
In the prior art, there are quick release mechanisms which do not require special shafts or modifications, but these mechanisms have important limitations. It is common, for instance, for prior art mechanisms to have an undesirable interaction between the radial angle of the operating handle about the axis of the shaft and the adjustment of the clamping range of the mechanism. That is, rotating the operating handle around on the shaft to be clamped or tensioned changes the pretension and clamping range of the quick release. It is desirable to have an operating handle which may be pointed in any direction, independent of the pretension and clamping range of the quick release.
U.S. Pat. No. 5,409,321 to Chan F. Chen (1995), for example, provides a quick releasing mechanism that requires a special "swing" or "latch" type bolt. The quick release mechanism requires a lifting pin which pierces the shaft to be clamped. This cannot ordinarily be done with existing shafts, and inherently links the direction of the operating handle's swing or "throw" to the radial angle of the shaft. For example, if the handle's swing direction or "throw" is changed to avoid an obstacle, the shaft is rotated, changing the pretension adjustment and clamp range of the quick release.
A common variation on the quick release of Chen uses a smooth cylindrical lifting pin piercing the shaft in much the same way as the pin of Chen. However, the pin is used as an axle on which a pair of cams is rotated. The cams are located symmetrically outboard of the shaft and are connected to a handle. When the handle is rotated or "thrown" about the pin, the cams act on the pin to force the end of the shaft outward relative to the surface of the cams. This tensions the shaft, gripping the object to be clamped between the surfaces of the cams and a nut or other means attached to the opposite end of the shaft.
Generally, a quick releasing mechanism with a lifting pin that pierces the shaft requires a pretension adjustment means, usually a threaded nut, be located on an opposite end of the shaft to be clamped. This is often undesirable, as it locates the adjustment means away from the quick release handle. If the shaft passes through a barrier, the opposite end of the shaft may be difficult to reach. This makes adjustment and operation of the quick release difficult.
What is needed is a quick release where the adjustment means is always easily reachable from the operating handle.
If the opposite end of the shaft is unreachable, as in the case of a blind shaft, the pierced shaft type of quick release is unusable unless the shaft is threaded into the blind hole. In this case, adjustment is still possible, but only by rotating the shaft. The resulting throw of the quick release handle is unpredictable and will depend on the pretension required, wear in the mechanism, and other factors that may change over time. What is needed is a quick release where the direction of handle throw is independent of the tension adjustment and inherent wear factors.
The pierced shaft type of quick release also has an undesirable second mode of use. People attempting to operate the quick release without understanding how it works may use the handle to simply turn the shaft, as if the handle were a short wrench. This produces a tightening action via the adjustment threads, but it is often insufficient to adequately tension the shaft. When the device to which the quick release is attached is used, the shaft may come loose. In the case of a wheel on a bicycle, for example, the results may be disastrous. What is needed is a quick release that cannot be improperly used as a crank.
Finally, quick release mechanisms of the pierced shaft type inherently block the end of the shaft to be clamped. This makes them unusable when access through the end of the shaft is required. For example, many internally geared bicycle hubs have hollow axles with shift chains or rods passing from the end of the shaft axially down into the shaft. The special end on the shaft shown in Chen would block the passage of any shift chains or rods. Even if the end of the shaft were modified, the pin piercing the shaft would block access through the center of the shaft. What is needed is a quick release that does not block access to the interior of the shaft along the axis of the shaft.
U.S. Pat. No. 5,556,222 to Chun-Hsung Chen (1996) and U.S. Pat. No. 5,156,508 to Grisley (1992) are representative of a class of quick release mechanisms where a lifting block or rod with opposed spindles is threadably attached to a shaft to be fastened. The shaft passes through the lifting block, and a pair of cams is mounted on the spindles symmetrically outboard of the shaft. The cams are connected to an operating handle. When the handle is rotated or "Trown" about the spindles, the cams act on the lifting block and force the end of the shaft outward relative to the surface of the cams. This tensions the shaft, gripping the object to be clamped between the surfaces of the cams and a nut or other means attached to the opposite end of the shaft.
Quick releases with a lifting block threadably attached to the shaft inherently link the pretension or clamp range to the direction of the operating handle's swing or "Throw". For example, if the handle's swing direction or throw is changed to avoid an obstacle, the lifting block is rotated relative to the shaft, changing the pretension and clamp range of the quick release. What is needed is a quick release where the throw and the tension adjustment are completely independent.
U.S. Pat. No. 5,156,508 to Grisley attempts to overcome this limitation by providing a variable thickness thrust plate which can be inserted between the cams and the object to be clamped. This reduces but does not eliminate the problem. What is needed is a quick release where all tension adjustment can be performed without shims.
Quick releases with a threadably attached lifting block also have the undesirable second mode of use as wrench or crank.
U.S. Pat. No. 2,043,125 to Stahl (1936) describes a quick release where an adjusting nut may be operated without interfering with the operation of the cam operated lifting means. A trunnion block with opposed trunnions is placed over a threaded shaft, followed by an adjusting nut. The clamp may be adjusted without having to move the handle.
The clamp of Stahl requires a washer which is not attached to the rest of the mechanism, creating an opportunity for the washer to be lost or be installed incorrectly. What is needed is a quick release which is self contained, and does not have parts to be lost or assembled incorrectly.
U.S. Pat. No. 5,476,020 to Garvey et al describes a cam operated quick release mechanism with a pair of coaxial inwardly pointing cam pins. The cam pins act to spread the distance between a pair of washers stacked on a bolt. The washers act outwards to clamp an object onto the bolt between a fixed end of the bolt and a threaded nut at the opposite end of the bolt.
The quick release of Garvey et al (1995) overcomes the problem of linking handle throw with pretension and clamp range. The handle may be rotated around the shaft without changing the tension adjustment. While solving this problem, the cam arrangement of Garvey limits the functional rotation of the handle to 90 degrees. This limits the net effective leverage of the mechanism to half that of a cam that operates through 180 degrees or more. What is needed is a quick release that uses more of the available throw room to reduce the forces required on the handle for a given clamp force.
Also, in the quick release of Garvey et al, rotating the operating handle radially about the shaft to be clamped will cause the cams to ride up on the cam tracks in the washers, separating the washers and creating drag on the handle. What is needed is a quick release where the handle can be rotated freely.
Additionally, the only thing keeping the cam pins of Garvey from spreading apart is the stiffness of the handle arms. If the handle must swing over a protruding end of the bolt, the arms must be elongated, making it difficult to provide the necessary lateral stiffness. What is needed is a quick release which provides positive retainment of the cams.
The quick release of Garvey also consists of three separate pieces that must be aligned before use. This is inconvenient and parts may be lost or misplaced when disassembled.
What is needed is a quick release that is self contained and permanently aligned, ready for use.
German Utility Model G08908870.0 (1989) describes a self contained quick release similar in operation to the quick release of Garvey. A pair of inward facing cam pins acts to separate a pair of washers. An integral nut with a raised tower is made part of the mechanism. The mechanism is intended for use with internally geared hubs on bicycles. The nut is adapted for passage of a shift chain through the interior of the mechanism.
This quick release solves many problems with prior art quick releases, but has several limitations. The handle operates over a comparatively small range of movement, reducing leverage and limiting the amount the clamp opens and closes. This makes the clamp adjustment very sensitive and the adjustment nut may have to be loosened to get enough clearance to remove the bicycle wheel from the bicycle. What is needed is a quick release with increased leverage and a larger clamping range.
Also, the width of the ends of the handle arms where the cams are formed is necessarily wide. This may interfere with existing objects in the vicinity of the quick release. The location of the pivot point of the handle is also very low, requiring the handle to lay close to the surface to be clamped. This again may interfere with objects in the vicinity. What is needed is a narrower quick release which allows the handle to avoid hitting objects in the vicinity.